Climate Change Skeptics

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Climate Change Skeptics


Climate change skeptics are those who doubt or disbelieve some aspect of the mainstream scientific view of global climate change or, in some cases, discount that view entirely. The mainstream or consensus view is that Earth is getting warmer; that human-released (anthropogenic) greenhouse gases, such as carbon dioxide and methane, are the main cause of today's warming; that global warming's consequences will be mostly negative; and that the future course of climate change can be influenced by human actions, such as burning less fossil fuel.

In science, skepticism is the principle that one should proportion one's belief in any claim to the available evidence—the weaker the evidence, the weaker the belief. In this sense, all scientists consider themselves skeptics, only some disagree about exactly what the evidence is and how it should be weighed. In this positive sense, some scientists are skeptical of certain aspects of the mainstream view of climate change. These scientific skeptics are a minority of the scientific community, but the work of dissidents or skeptics is often an essential part of the scientific process.

A much larger group of climate change skeptics consists of individuals with little or no scientific expertise. These persons, who have decided that global warming is a hoax, exaggeration, or delusion, tend to be interested only in those fragments of scientific literature that appear, in isolation, to support their predetermined views. These persons are often termed deniers rather than skeptics, as they tend to ignore or deny scientific knowledge.

Historical Background and Scientific Foundations

Scientific disputes about changing climate have gone on since the 1970s, when theories of a new ice age (global cooling) were competing with theories of global warming. In the 1980s, scientific opinion solidified around the concept of global warming. By the early 1990s, warming was considered a present fact or future

possibility by most climate and weather scientists. By the late 1990s, the great majority of scientists with relevant qualifications agreed that global climate change is real, is caused primarily by human activity, and might be mitigated (made less serious) by reducing emissions of greenhouse gases, especially carbon dioxide.

Disbelief or doubt about climate change occurs on a spectrum, from authentic scientific doubt to irrational denial or misuse of scientific evidence. Today, a small minority of scientists with expertise in climate or weather science maintain that global warming is not happening or that the observed warming is not human-caused. Many scientists disagree about climate-science details such as the range of uncertainty that should be assigned to predictions of future sea-level rise. A large number of nonscientific voices can be found on the Internet, in opinion columns, on radio and television, and in political circles who claim that climate change is a hoax, fantasy, or scare tactic invented by environmentalists. These nonscientific voices have had almost no influence on the scientific world, but have been successful in confusing public perceptions of global-warming science.

Climate-Change Skepticism and Denial among Non-Scientists

Public Opinion. Climate change was not widely discussed by nonscientists until the early 1970s, when the environmental movement was raising general concern about global harm caused by technology (pollution, extinction, etc.). The public was confused later in the 1970s by scientific debate over whether Earth might, in fact, be entering a new ice age rather than facing global warming. The ice-age theory received significant media coverage, but by the end of the decade had been rejected by scientists in favor of global warming. By the 1990s, polls found that about half of Americans thought that global warming was already happening or would soon happen; only about one in eight thought it would never happen. Levels of climate-change concern actually dipped in the early 2000s, with only about one-third of polled Americans saying they worried “a great deal” about climate change.


ANTHROPOGENIC: Made by people or resulting from human activities. Usually used in the context of emissions that are produced as a result of human activities.

FOSSIL FUEL: Fuel formed by biological processes and transformed into solid or fluid minerals over geological time. Fossil fuels include coal, petroleum, and natural gas. Fossil fuels are non-renewable on the timescale of human civilization, because their natural replenishment would take many millions of years.

GREENHOUSE GASES: Gases that cause Earth to retain more thermal energy by absorbing infrared light emitted by Earth's surface. The most important greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and various artificial chemicals such as chlorofluorocarbons. All but the latter are naturally occurring, but human activity over the last several centuries has significantly increased the amounts of carbon dioxide, methane, and nitrous oxide in Earth's atmosphere, causing global warming and global climate change.

HOCKEY STICK CONTROVERSY: Controversy from 1998 to approximately 2006 over the validity of the hockey-stick graph, a chart of global average air temperatures indicating that recent climate warming is unprecedented for at least the last 1,100 years or so. Critics argued the graph was flawed and misleading, but in 2006, after a careful review of the evidence, the National Academy of Sciences affirmed that the graph is essentially accurate, though its shape is less certain for earlier dates.

ICE AGE: Period of glacial advance.

INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE (IPCC): Panel of scientists established by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) in 1988 to assess the science, technology, and socioeconomic information needed to understand the risk of human-induced climate change.

SKEPTICISM: Doubt about the truth of a claim. Skepticism, as opposed to denialism, may have a reasonable basis: in fact, skepticism is essential to the scientific process of discovering new knowledge, in which claims are carefully tested before being accepted as correct.

URBAN HEAT ISLAND: Area of warm weather in and immediately around a built-up area. Pavement and buildings absorb solar energy while being little cooled by evaporation compared to vegetation-covered ground. Skeptics of global climate change at one time argued that the expansion of urban heat islands near and around weather stations has caused an illusion of global warming by biasing temperature measurements. Although urban heat islands do exist, the argument that they produce an illusion of global warming has been discredited.

After 2004, concern rose again. Concern about global warming appears to be associated with political beliefs, with political conservatives being less likely to credit mainstream scientific views. In 2007, a Gallup poll found that about 59% of independents were worried about global warming, 75% of Democrats, and 34% of Republicans. European public opinion generally matched U.S. opinion until the late 1990s, but since then there has been an increase of belief in climate change outside the United States. A 2003 survey of 19 non-U.S. countries by the Pew Research Center found 81% of respondents very concerned about global climate change.

Nonscientist Commentators. Statements that global warming is unreal, is not caused by humans, or is not dangerous even if it is real are often made by nonscientists on radio, television, and the Internet or in print. The most common misuse of science by such commentators is selective citation of studies that appear to support the speaker's predetermined opinion, coupled with silence about the much greater quantities of data supporting mainstream scientific views. Definitely incorrect claims are also sometimes made, such as the statement that computerized climate models ignore water vapor. This claim was made, for example, by columnist Alexander Cockburn in The Nation on May 14, 2007: “Water is exactly that component of the Earth's heat balance that the global warming computer models fail to account for.” Because of the access to public attention that some of these speakers enjoy, their opinions often reach a larger public than do views expressed by qualified scientists.

Claims that global warming is a hoax, plot, or illusion come from voices across the political spectrum. Alexander Cockburn, the left-wing journalist already mentioned, states: “There is still zero empirical evidence that anthropogenic production of carbon dioxide is making any measurable contribution to the world's present warming trend. The greenhouse fearmongers rely on unverified, crudely oversimplified models to finger mankind's sinful contribution.” In reality, there is mounting evidence from many different sources that anthropogenic climate change is occurring. This evidence is described in detail in the Inter-governmental Panel on Climate Change (IPCC)'s report Climate Change 2007: The Physical Science Basis. Also, computer climate models are not “unverified, [and] crudely oversimplified” but increasingly accurate and constantly tested against real-world data.

The majority of anti-climate-change political commentators are political conservatives. The list of prominent climate skeptics or deniers who self-identify as conservative includes, for example, William Buckley, George Will, and Anne Coulter. Will has recalled media excitement over the possibility of global cooling in the 1970s and mocked recent scientific work showing wild-life species ranges are being shifted by global warming (Washington Post, December 22, 2004; April 2, 2006). Often, such commentators will claim that mainstream scientific opinion is actually on their side. Coulter claimed in 2007 that “[t]here are more reputable scientists defending astrology than defending ‘global warming’” (Human Events, February 28, 2007). Similarly, Bonner Cohen, senior fellow at the National Center for Public Policy Research, stated on C-SPAN in 2006 that “if you go to climate scientists, climatologists, the people who look at this, as opposed to the scientific community at large, you will find absolutely no consensus…. The vast majority of them are somewhat agnostic on the whole thing” (video and transcript at; see Bibliography).

There is, contrary to these statements, a strong consensus among climate scientists in favor of the reality and human-caused nature of climate change. An article by Naomi Oreskes in the December 3, 2004 issue of Science noted that every major scientific body in the United States whose members' specialization is relevant to climate change, such as the American Meteorological Association, has issued a statement affirming the consensus scientific view. Oreskes also surveyed 928 articles discussing climate change published from 1993 to 2003—all those in the Institute for Scientific Information database mentioning “climate change” in their abstracts. Seventy-five percent of these articles explicitly or implicitly accepted the consensus position and not one disagreed with it. Other surveys of scientific opinion have also found large majorities in support of the consensus position.

Another prominent conservative opponent of climate change is Rush Limbaugh, a syndicated radio, television, and print columnist with a weekly radio audience of more than 10 million listeners. Limbaugh denies that human activity has damaged the ozone layer and that present-day climate change is human-caused. For example, he has written that a “fact you never hear the environmentalist wacko crowd acknowledge is that 96 percent of the so-called ‘greenhouse’ gases are not created by man, but by nature” (Limbaugh, 1993). Yet the IPCC's regular reports on climate change since 1990, along with scores of other books and articles about climate change, do make it clear that most of the carbon dioxide, water vapor, methane, and other greenhouse gases in the atmosphere are natural in origin—indeed, essential to keeping Earth warm enough to support human life. The issue has never been whether human beings are responsible for most of the greenhouse gases put into the atmosphere, but whether they are adding enough to cause significant change in the global climate. Most climate and weather scientists agree that they are.

Fiction writer Michael Crichton has also reached a wide public with his anti-climate change message. In Crichton's bestselling 2004 novel State of Fear, evil environmentalists conspire to create apparently natural disasters and other evidence to cause panic over global warming. Crichton's book, which claimed to be based on science, was heavily criticized by climate scientists, but did receive a journalism award from the American Society of Petroleum Geologists, the only scientific society in the world to have adopted an official statement in denial of anthropogenic global climate change. Most of the society's members are employed by the oil industry, which has opposed the scientific consensus view of climate change.

Industry Funding of Climate Change Denial. Corporations seeking to influence public opinion against climate change have funded nonscientific groups that deny climate change. In 2006, the United Kingdom's national scientific academy, the Royal Society (the equivalent of the National Academy of Sciences) announced that the oil company ExxonMobil had distributed several million dollars to 36 groups in the United States alone. These groups, the society said in a letter to ExxonMobil, “have been misinforming the public about the science of climate change.” The Union of Concerned Scientists reported in 2007 that ExxonMobil had spent a total of $16 million to fund denial groups and create public confusion about climate change.

As a result of this negative publicity, ExxonMobil softened its anti-climate change stance in 2007. In February, the company's vice president for public affairs, Kenneth P. Cohen, said ExxonMobil had never denied climate change, that “the global ecosystem is showing signs of warming, particularly in polar areas,” and that “the appropriate debate isn't on whether the climate is changing but rather should be on what we should be doing about it.” The company reportedly cut off funding in 2006 to at least one denial group, the American Enterprise Institute, which received over $1.8 million from ExxonMobil from 1998 to 2006. In early 2007, the American Enterprise Institute offered $10,000 to any scientist who would produce a paper undermining the IPCC's report Climate Change 2007:The Physical Science Basis. It was not yet known, as of late 2007, if there would be any takers.

Climate-Change Skepticism from Scientists

A few scientists have disputed the reality or anthropogenic nature of global climate change. Such skeptics, including economist Ross McKitrick and minerals consultant Steven McIntyre, have raised a number of arguments against global warming. For example, they have argued that the famous “hockey stick” graph showing that recent global temperatures are much greater than those for the last 1,000 years, which featured prominently in Al Gore's hit documentary An Inconvenient Truth, is flawed. They have also pointed to disagreement between surface measurements of Earth's temperature and satellite measurements, which seemed to show that Earth's atmosphere had actually cooled. Some have argued that changes in the sun's heat output, not anthropogenic greenhouse gases, are responsible for global warming, and that warming measurements have been exaggerated because they are made in the vicinity of hot spots created by the pavement and buildings of large cities, “urban heat islands.”

In the early 2000s, however, most of these scientific uncertainties collapsed under the weight of new scientific evidence. The U.S. Congress charged the U.S. National Research Council with investigating the merits of the hockey stick graph, which had also appeared in expert testimony to Congress. In 2006, the council affirmed the basic validity of the famous graph. Although the statistical mathematical methods used in producing the graph were found to be inadequate, replacing them with correct methods did not change the graph's shape. The data show that today's global warming is unprecedented in the last 1,000 years.

A 2005 study commissioned specifically to look into the puzzle of the satellite data found that the data had originally been analyzed incorrectly. When the analytical errors were fixed, the apparent contradiction disappeared. Again, it was verified that Earth is indeed warming. Urban heat islands and solar variation have also both been ruled out as explanations of global warming by peer-reviewed scientific studies conducted in recent years.

Some scientists continue to disagree with estimates of the magnitude of future climate change. John Christy, a climatologist at the University of Alabama, said in 2007, “don't sign me up for that catastrophic view of climate change” (quoted in Nature, February 8, 2007). Another example is Christopher Landsea, a meteorolo-gist at the U.S. National Hurricane Center, who announced in 2005 that he was withdrawing from the IPCC on the grounds that he had “come to view the part of the IPCC to which my expertise is relevant as having become politicized.” In particular, he claimed that fellow lead author Kevin Trenberth used his IPCC position to “promulgate to the media and general public his own opinion that the busy 2004 hurricane season was caused by global warming, which is in direct opposition to research written in the field and is counter to conclusions” in the IPCC's 2001 Assessment Report. Landsea has argued that global warming has not yet affected hurricane activity detectably and that “studies that any impact in the future from global warming upon hurricane[s] will likely be quite small.”

The 2007 IPCC report did not, ultimately, assert that anthropogenic global warming is definitely responsible for increased hurricane frequency or severity. Since the report came out, however, scientists have published data showing that hurricane intensity and frequency may indeed have increased over the last century as a result of anthropogenic ocean warming. The relationship between hurricanes and global warming is a point on which authentic scientific disagreement continues.

Impacts and Issues

Studies have been conducted to resolve questions raised by scientific skeptics of climate change—a direct benefit to the scientific process. Many disputes have now been resolved in favor of the mainstream or consensus scientific view of climate change. As of 2007, scientific skepticism about the main elements of the climate-change consensus appeared to be decreasing. Some critics were shifting their focus from arguing that climate change is not real to arguing that it would be too expensive to take action to mitigate it. However, with the release of the third part of the IPCC's latest climate report Climate Change 2007: Mitigation of Climate Change, these critics again found themselves on the outside of a widely supported scientific consensus. The IPCC report contends that greenhouse gas concentrations in the atmosphere could be stabilized at low cost or possibly even at a profit.

Internet-based attacks on the consensus scientific view continued unabated even after the release of the 2007 IPCC report, as did mockery by nonscientific commentators, such as Cockburn, Coulter, and Limbaugh. The response of public opinion to the climate-change issue will depend on the quality of media and educational coverage of mainstream science and on how apparent the effects of climate change are to people in daily life.

Primary Source Connection

An overwhelming majority of the scientific community accepts global climate change theories. The following article notes that while researchers continue to debate— typically within a consensus range—about smaller aspects of climate change theory, scientific skepticism of human-influenced climate change is increasingly rare.


Some scientists who question whether human-caused global warming poses a threat have long pointed to records that showed the atmosphere's lowest layer, the troposphere, had not warmed over the last two decades and had cooled in the tropics.

Now two independent studies have found errors in the complicated calculations used to generate the old temperature records, which involved stitching together data from thousands of weather balloons lofted around the world and a series of short-lived weather satellites.

A third study shows that when the errors are taken into account, the troposphere actually got warmer. Moreover, that warming trend largely agrees with the warmer surface temperatures that have been recorded and conforms to predictions in recent computer models.

The three papers were published yesterday in the online edition of the journal Science.

The scientists who developed the original troposphere temperature records from satellite data, John R. Christy and Roy W. Spencer of the University of Alabama in Huntsville, conceded yesterday that they had made a mistake but said that their revised calculations still produced a warming rate too small to be a concern.

“Our view hasn't changed,” Dr. Christy said. “We still have this modest warming.”


According to the National Academy of Sciences: “The fact is that Earth's climate is always changing. A key question is how much of the observed warming is due to human activities and how much is due to natural variability in the climate. In the judgment of most climate scientists, Earth's warming in recent decades has been caused primarily by human activities that have increased the amount of greenhouse gases in the atmosphere [figure omitted]. Greenhouse gases have increased significantly since the Industrial Revolution, mostly from the burning of fossil fuels for energy, industrial processes, and transportation. Greenhouse gases are at their highest levels in at least 400,000 years and continue to rise.”

“Global warming could bring good news for some parts of the world, such as longer growing seasons and milder winters. Unfortunately, it could bring bad news for a much higher percentage of the world's people. Those in coastal communities, many in developing nations, will likely experience increased flooding due to sea-level rise and more severe storms and surges. In the Arctic regions, where temperatures have increased almost twice as much as the global average, the landscape and ecosystems are rapidly changing.”

“Although the potential effects of climate change are widely acknowledged, there is still legitimate debate regarding how large, how fast, and where these effects will be. Climate science is just beginning to project how climate change might affect regional weather. Estimating climate change impacts also requires projecting society's future actions, particularly in the areas of population growth, economic growth, and energy use.”

SOURCE:Staudt, Amanda, Nancy Huddleston, and Sandi Rudenstein. Understanding and Responding to Climate Change. National Academy of Sciences, 2006.

Other climate experts, however, said that the new studies were very significant, effectively resolving a puzzle that had been used by opponents of curbs on heat-trapping greenhouse gases.

“These papers should lay to rest once and for all the claims by John Christy and other global warming skeptics that a disagreement between tropospheric and surface temperature trends means that there are problems with surface temperature records or with climate models,” said Alan Robock, a meteorologist at Rutgers University.

The findings will be featured in a report on temperature trends in the lower atmosphere that is the first product to emerge from the Bush administration's 10-year program intended to resolve uncertainties in climate science.

Several scientists involved in the new studies said that the government climate program, by forcing everyone involved to meet five times, had helped generate the new findings.

“It felt like a boxing ring on occasion,” said Peter W. Thorne, an expert on the weather balloon data at the Hadley Center for Climate Prediction and Research in Britain and an author of one of the studies.

Temperatures at thousands of places across the surface of the earth have been measured for generations. But far fewer measurements have been made of temperatures in the air from the surface through the troposphere, which extends up about five miles.

Until recently Dr. Christy and Dr. Spencer were the only scientists who had plowed through vast volumes of data from weather satellites to see if they could indirectly deduce the temperature of several layers within the troposphere.

They and other scientists have also tried to analyze temperature readings gathered by some 700 weather balloons lofted twice a day around the world.

But each of those efforts has been fraught with complexities and uncertainties.

The satellites' orbits shift and sink over time, their instruments are affected by sunlight and darkness, and data from a succession of satellites has to be calibrated to account for eccentricities of sensitive instruments.

Starting around 2001, the satellite data and methods of Dr. Christy and Dr. Spencer were re-examined by Carl A. Mears and Frank J. Wentz, scientists at Remote Sensing Systems, a company in Santa Rosa, Calif., that does satellite data analysis for NASA.

They and several other teams have since found more significant warming trends than the original estimate.

But the new paper, by Dr. Mears and Dr. Wentz, identifies a fresh error in the original calculations that, more firmly than ever, showed warming in the troposphere, particularly in the tropics.

The error, in a calculation used to adjust for the drift of the satellites, was disclosed to the University of Alabama scientists at one of the government-run meetings this year, Dr. Christy said.

The new analysis of data from weather balloons examined just one possible source of error, the direct heating of the instruments by the sun.

It found that when data were examined in a way that accounted for that effect, the temperature record produced a warming, particularly in the tropics, again putting the data in line with theory.

“Things being debated now are details about the models,” said Steven Sherwood, the lead author of the paper on the balloon data and an atmospheric physicist at Yale. “Nobody is debating any more that significant climate changes are coming.”

Andrew C. Revkin

revkin, andrew c. “errors cited in assessing climate data.” the new york times august12, 2005.

See Also Hockey Stick Controversy; IPCC Climate Change 2007 Report: Criticism; IPCC Climate Change 2007 Report: Physical Science Basis; Media Influences: False Balance; Public Opinion; Urban Heat Islands.



Crichton, Michael. State of Fear: A Novel. New York: HarperCollins, 2004.

Limbaugh III, Rush H. See, I Told You So. New York: Pocket Books, 1993.

Metz, B., et al, eds. Climate Change 2007: Mitigation of Climate Change: Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Solomon, S., et al, eds. Climate Change 2007: The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.

Weart, Spencer R. The Discovery of Global Warming. Cambridge, MA: Harvard University Press, 2003.


Begley, Sharon. “Global-Warming Deniers: A Well-Funded Machine.” Newsweek (March 18, 2007).

Cockburn, Alexander. “Is Global Warming a Sin?” The Nation (May 14, 2007).

Hopking, Michael. “Climate Skeptics Switch Focus to Economics.” Nature 445 (February 8, 2007): 582–583.

Mahlman, J. D. “Science and Nonscience Concerning Human-Caused Climate Warming.” AnnualReview of Energy and the Environment 23 (1998): 83–105.

Mufson, Steven. “ExxonMobil Warming Up to Global Climate Issue.” Washington Post (February 10, 2007).

Oreskes, Naomi. “The Scientific Consensus on Climate Change.” Science 306 (December 3, 2004): 1686.

Revkin, Andrew C. “Errors Cited in Assessing Climate Data.” The New York Times (August 12, 2005).

Sample, Ian. “Scientists Offered Cash to Dispute Climate Study.” The Guardian (February 2, 2007).

Will, George. “Global Warming? Hot Air.” The Washington Post (December 23, 2004).

Will, George. “Let Cooler Heads Prevail.” The Washington Post (April 2, 2006).

Web Sites

Coulter, Anne. “Let Them Eat Tofu!” Human Events, February 28, 2007. <> (accessed December 5, 2007).

“Industry-Backed Author: The ‘Vast Majority’ of Climatologists Don't Believe in Global Warming.”, August 9, 2006. <> (accessed December 5, 2007).

Landsea, Christopher. “An Open Letter to the Community from Chris Landsea,” January 17, 2005. <> (accessed August 13, 2007).

Mooney, Kevin. “UN Climate Summary Designed to Dupe, Critics Say.” Cybercast News Service, February 2, 2007. <> (accessed August 13, 2007).

Larry Gilman